I constructed this sound to light converter as a final project in one of my ELT courses.
It's a 3 band (high, mid, low) converter utilizing 2 LM1458N opamp ICs and a series of RC filters. The circuit is based on a Forrest Mims design. I modified the capacitor and resistor values a little to alter the cutoff frequencies. I also embelished with the lexan case, dual LEDs (mimics a stereo signal), and the power switch.
The circuit was prototyped on a breadboard and then transferred to the solder board.
A shop power supply was used for testing, but I wanted the unit to be completely portable when hooking up an Ipod or cellphone. I used 2 -9 volt batteries in series for the supply, that led to the addition of the switch to conserve battery voltage.
I mounted the LEDs on a scrap of white plexi (the kind used for backlit signs).